1. Field of the Invention
This invention relates to the field of bubble memory devices and in particular to the amorphous bubble type.
2. Description of the Prior Art
The fabrication of present day amorphous bubble films has followed the prior art process for the fabrication of conventional (i.e., crystalline) garnet films. This prior art process generally comprises depositing a bubble film at a relatively high temperature on top of a non-magnetic substrate. An insulator overlay is then placed over the bubble film after which a permalloy film, which is utilized for the magnetic field access circuitry, is deposited. This permalloy film is deposited at a lower temperature than the bubble film deposition, but nevertheless at a high temperature.
When the above process is applied to the amorphous bubble devices, several problems have been encountered by the prior art. In contrast to garnet films, amorphous films must be deposited at a relatively low temperature. Therefore, subsequent processing after the amorphous film has been deposited on a substrate must be done at low temperatures to prevent the amorphous films from crystallizing. This leads to several undesirable features in the permalloy drive layer in that the permalloy films tend to exhibit poor adhesion and high coercivity. One approach to avoiding these problems has been to use Ni Fe laminates. This multilayer structure is considerably more complicated so that the remedies have tended to complicate the permalloy structure. This complication has been evidenced by the paper "Electron-Beam Fabrication of High-Density Amorphous Devices," IEEE Trans. Mag 11, 1142 (1975).